Light concentration using hetero-junctions of anisotropic low permittivity metamaterials

Abstract

Focusing incident power into an area of high concentration is of significant interest for various applications. In optics, this has been traditionally achieved with lenses where a higher curvature and lens permittivity typically result in shorter focal distances (low f/D). In this work, we present designs and techniques for collecting, refracting and guiding incident light into an area of high power concentration (a hot spot) at extremely short distances. Specifically, a flat low-profile focusing mechanism is presented using a hetero-junction of anisotropic metamaterials (MTMs). The hetero-junction is formed from two cleaved finite slabs of low (near zero) permittivity anisotropic MTMs with rotated optical axes. The MTMs have near zero longitudinal permittivity while matched in the transverse direction. Such MTMs are shown to provide a unique ability to bend the transverse magnetic or p-polarized light away from the normal and along the interface, contrary to conventional dielectrics, and with minimal reflections; hence allowing for a low profile design. Realizations in the optical regime are presented using periodic bilayers of metal and dielectric. The proposed hetero-junction focusing device concentrates the normally incident plane wave and/or beam into a corresponding focal region similar to a lens via multiple refractions. The hetero-junction is capable of creating a hot spot very close to the device, much closer than dielectric lenses and it significantly outperforms the size requirements of thick high curvature lenses with low f/D ratios. The proposed designs can find applications in various scenarios including solar and thermo photovoltaics, photodetectors, concentrated photovoltaics, non-imaging optics, micro-and nano-Fresnel lenses.

Functional Metamirrors Using Bianisotropic Elements

“…The unprecedentedly short focal length of our metalens is significantly smaller than those of conventional and other metamaterialbased lenses 10,12,31 . Similar strong focusing abilities have been recently achieved with a lens based on hetero-junctions of anisotropic metamaterials 32 . However, that construction is optically thick and generally operates only with incident TM-polarized light, which reduces the efficiency of the lens.…”

Transforming the cost of solar-to-electrical energy conversion: Integrating thin-film GaAs solar cells with non-tracking mini-concentrators

“…As an alternative to simply improving PCE, solar concentrators have been demonstrated as a means for reducing the use of costly active solar cell materials. 14,15 However, most concentrators suffer from a significant roll-off in efficiency at large light incident angles and can also result in high cell operating temperatures, thereby necessitating expensive active solar tracking and solar cell cooling systems. 16 Here, we demonstrate that thin-film GaAs solar cells produced by an accelerated non-destructive ELO (ND-ELO) fabrication process that are integrated with simple thermoformed mini-concentrators can lead to a dramatic reduction in the cost of the production of electricity via solar energy harvesting.…”

Dirac leaky-wave antennas for continuous beam scanning from photonic crystals

“…It has even been proposed that ENZs can enable electric levitation of a dipole 9 . The directive emission (gain enhancement) using bulk ZIMs, as well as the atypical bending of light using ZIMs 7 , are primarily owing to Snell's law. Air has a higher refractive index than the ZIM, hence the angle of refraction in air is smaller than in the ZIM, contrary to typical dielectrics.…”

“…Z ero-index metamaterials (ZIMs), including epsilon-nearzero (ENZ) metamaterials 1 , offer unique and fascinating wave phenomena such as tunnelling of waves through channels and bends 2,3 , tailoring the phase of the radiation patterns from arbitrary sources 4 , directive emission of sources 5,6 and unusual bending of light for extremely short focusing 7 , to name a few. It is also possible to enhance and shape the air-side radiation patterns of radiators by placing them on (an)isotropic ENZs and ZIMs 8 .…”